Alkaline earth sulfides, doped with rare earth ions, are the basis of a large class of electroluminescent displays. Traditionally, thin films of alkaline earth sulfides have been prepared by sputtering, evaporation, or metal organic chemical vapor deposition (MOCVD). Sputtered films suffer from a substantial amount of nonstoichiometry. To overcome this nonstoichiometry, sulfur co-evaporation and sputtering in a reactive atmosphere (H.sub.2 S) must be used to improve the quality of the layers.
MOCVD techniques that overcome the problems encountered with sputtering have shown promise for growing layers of alkaline earth sulfides. However, these techniques grow a film one layer at a time. Each monolayer is deposited is a sequence of steps. For example, to deposit a layer of ZnS or SrS on a substrate, dimethylzinc is introduced in the vapor phase over the substrate and forms zinc bonds on the substrate surface. The source of dimethylzinc vapor is then turned off and excess unreacted dimethylzinc is removed from the reactor by H.sub.2 gas purge. H.sub.2 S is then introduced into the reactor and reacts with the dimethylzinc that was absorbed onto the substrate to form a layer of ZnS. The excess H.sub.2 S is then purged and the cycle repeated. To grow a layer with a useful thickness, hundreds of cycles are needed. Hence, this method is poorly suited to large scale protection of display devices. In addition, the method requires H.sub.2 S which is a highly toxic compound, and hence, is to be avoided if possible.
Broadly, it is the object of the present invention to provide an improved method for a depositing layer of metal sulfide.
It is a further object of the present invention to provide a method for depositing a layer of an alkaline earth sulfide by a continuous deposition process that does not require a large number of repeated cycles.
It is a still further object of the present invention to provide a method for depositing a layer of alkaline earth sulfide that does not require the use of H.sub.2 S.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.